(1) Field of the Invention
The present invention relates to a system and method for communicating data between control units such as an engine control unit in an automotive vehicle and a master station diagnosing a selected control unit.
(2) Background Art
Recently, along with development in semiconductor technology, various parts of vehicles are being controlled electronically. Many vehicles are now equipped with microprocessors functioning as electronic control units (ECUs), for engine control, as one example.
Such advanced electronically controlled systems provide high performance and can enhance rider comfort in vehicles, but faults in such systems are very difficult to diagnose. Since a large volume of input signals are subject to complex electronic processing, it is difficult to trace causal relationships between generated phenomena and their causes. In addition, a high level of knowledge is required to analyze these phenomena. Furthermore, intermittent disconnections of minute electrical signals are susceptible to external electrical noises which will affect results of analysis in the generated phenomena.
In a system where each electronic control unit is diagnosed by the master station, the master station selects a desired electronic control unit to be diagnosed, from a plurality of electronic control units which may be present in a vehicle, transmits a diagnostic control command to the selected electronic control unit, and receives reply data from the electronic control unit. In this data communication, the master station initializes a communication line between the master station and each electronic control unit and transmits an initialize command to set each of the electronic control units in a stand-by state, waiting for reception of a system select command which selects the desired electronic control unit from among the plurality of electronic control units to establish a data link between the master station and a particular electronic control unit.
Then, when a data link is established between the master station and the selected electronic control unit, the master station transmits a control command such as a parameter set command to carry out a desired control operation and, after the transmission of the control command, transmits continuously two information bytes related to the control command with predetermined intervals provided. The first information byte sets an item to be controlled, and the second information byte sets a controlled variable of the item to be controlled. Thereafter, the master station transmits an execution command, monitors response performance of the vehicle, specifically, the engine with respect to a set state, thereby carrying out the diagnoses.
Termination of the diagnosis is carried out when the master station transmits a termination (end) command.
As described above, in an electronic control unit in which a data link is established with the master station, modification in the control state and output of the internal data are carried out in accordance with a control command issued from the master station and an information byte. These control operations are carried out until an end command is received from the master station.
However, data communication between the master station and the electronic control unit is carried out via signal transmission lines and connectors, and, therefore, inconvenience often occurs in a case where a connector which connects the master station and the selected control unit is disconnected after the control operation of the electronic control unit is modified by means of the control command derived from, e.g., the master station.
That is to say, since each control unit has no detecting means for detecting the connection state of the related connector, the control unit cannot detect the state where the connector is disconnected. This type of disconnection occurs frequently as many master stations are of a portable type and connection with the control unit is affected by an operator merely holding the connector in place, this makes it easy for the connection to be inadvertently interrupted or broken. If a control operation is initiated immediately before the connector is disconnected, in order to release this control operation, the connector must again be connected and the end command must be transmitted from the master station, or hardware resetting by means of a power switch is required.
Furthermore, since the control operation when the connector is disconnected is set in order to perform the failure diagnosis or analysis, the vehicle may be set in a running condition which is extreme compared to that required for the normal running. If a connection is broken after initiation of a control command, the vehicle will maintain its running condition according to the command until the connection is resumed and an end command is received. Therefore, an improvement has been desired since it is not desirable to leave the vehicle in such a controlled state for an extended period of time.
In systems employing a plurality of control units, control information generated by the operation of one control unit may cause one of the other control units in the vehicle to spontaneously change its controlled state according to the information.
In a case where, after initialization, the master station selects one of the control units, for example an engine control unit, to be diagnosed (hereinafter, referred to as the electronic control unit A), the master station diagnoses whether a control in the electronic control unit is normally carried out and then reads the internal data indicating the controlled state of the electronic control unit A. Next, after reinitialization is carried out (initialization being required between testing of each control unit), a control parameter of the next electronic control unit, for example an air conditioner control unit (hereinafter, referred to as electronic control unit B), is set to a desired value. However, diagnoses of control unit B has an influence on the controlled state of the electronic control unit A and so, after completion of checking control unit B, after which reinitialization is again required, the master station again reads the internal data of the control unit A and checks how the internal data has been varied after and before the setting of the control parameter of the electronic control unit B.
However, even though a value of the control parameter of the control unit B is modified as described above, and electronic control unit A is again checked, the value of the control parameter of the electronic control unit B after initialization is returned to the initial value in order to again select the control unit A. Therefore, since one control unit must be reset before checking of the next control unit, disadvantages occur such that the internal data of electronic control unit A cannot be read at the time when the control parameter for the control unit B is modified, thus making the causal relationships between the control units in a vehicular system hard to trace. This makes diagnoses of the units, as they interactively behave under actual driving conditions, difficult.